Italian external quality assessment scheme in immunoassay.

: This paper deals with the organization, the data processing and some of the results obtained in Italian external quality assessment (EQA) schemes for hormones, tumor markers and hepatitis B markers. The EQA for hormones and tumor markers includes up to sixteen analytes together with the participation, in 1990, of about 250 laboratories. Laboratory results were used to prepare periodic and end-of-period reports. The former includes the results (with the related statistical parameters) obtained by all participants and by laboratories using the same method, as well as the histogram of the data. The end-of-period report contains estimates of imprecision and average bias for all laboratories, for each laboratory and for the more widely employed kits. From 1980 to 1988, laboratory variability improved significantly for TSH, progesterone, estradiol, testosterone, CEA and ferritin, slightly for cortisol, FSH, prolactin and AFP, while there was no improvement for both total T3 and T4. For LH we found an unusually high variability mainly due to systematic differences between kits based on different monoclonal antibodies. About 200 laboratories participated in the EQA for hepatitis B markers (HBsAg and anti-HBs) organized in 1990. For these analytes the periodic reports show the percentage of negative and positive results and the histogram of the responses (absorbance or counts) normalized with respect to the cut off.